Conventionally, an article transport apparatus for an article storage system includes a stacker crane (mobile body) having a fork device (article transfer device) for transporting articles between an article receiving table (loading station) and a plurality of article storage units in storage racks. When causing the stacker crane to run toward the article receiving table, operation control means carries out a loading travel control for running the stacker crane to an article transfer position opposed to the article receiving table as a target stopping position, based on information from position detecting means that detects positions on a traveling path of the stacker crane. When running the stacker crane toward an article storage unit to which an article is to be transferred, among the plurality of article storage units, the operation control means carries out a storage running control for running the stacker crane to an article transfer position opposed to that article storage unit as a target stopping position, based on information from the position detecting means. (See Japanese Patent Publication (Unexamined) No. 2004-157885, for example.)
The position of an article placed on the article receiving table is variable in a traveling direction of the stacker crane due to a misalignment occurring when the article is supplied from outside by a forklift or the like. Consequently, when the article is transferred under a loading transfer control from the article receiving table to the stacker crane located in the article transfer position opposed to the article receiving table, the position relative to the stacker crane of the article transferred will also vary in the traveling direction of the stacker crane.
The position opposed to the article receiving table where the stacker crane stops under the loading travel control may vary in the traveling direction of the stacker crane from the predetermined article transfer position opposed to the article receiving table. In this case also, when an article is transferred under the loading transfer control from the article receiving table to the stacker crane, the position relative to the stacker crane of the article transferred will also vary in the traveling direction of the stacker crane.
When the position relative to the stacker crane of the article transferred to the stacker crane varies in the traveling direction of the stacker crane as noted above, even though the stacker crane is stopped accurately in an article transfer position for an article storage unit which is the destination of the article, the position of the article held by the stacker crane will vary in the traveling direction of the stacker crane from a proper position relative to the article storage unit, that is, a position where the middle of the article in the traveling direction of the stacker crane coincides with the middle of the article storage unit in the traveling direction of the stacker crane. In order to store the article deviating in the traveling direction of the stacker crane from a proper position relative to an article storage unit, in the article storage unit under the storing transfer control, while avoiding contact between the article and storage rack, for example, the plurality of article storage units need to have a sufficient length along the traveling direction of the stacker crane to allow for variations in the position of the article, and variations in the article transfer position, where the stacker crane stops, relative to an article storage unit which is the destination of the article. As a result, the storage rack has an increased length in the traveling direction of the stacker crane, which leads to an increase in the manufacturing cost of the storage rack and an enlarged installation space of the article storage system. Further disadvantages are that an increase in the traveling distance of the stacker crane lowers transporting efficiency and increases running cost.